A commonly used treatment for diseases, such as cancer or those caused by pathogen-infection, is the administration of drugs, e.g., chemotherapeutics and antibiotics. In order to kill the diseased cells, the drug(s) must enter the cells and reach an effective dose so as to interfere with essential biochemical pathways. However, some cells evade being killed by the drug by developing resistance to it (termed “drug resistance”). Moreover, in some cases, cancer cells (also called tumor cells or neoplastic cells) and damaged cells (e.g., pathogen-infected cells), or the pathogens themselves, develop resistance to a broad spectrum of drugs, including drugs that were not originally used for treatment. This phenomenon is termed “multidrug resistance” (MDR). For example, some cancer cells in a tumor evade being killed by chemotherapeutic drugs by becoming multidrug resistant to a broad spectrum of chemotherapeutic drugs, including drugs that were not originally used for treatment.
Patient cross-resistance to different anti-microbial and anti-cancer agents, which are structurally and functionally distinct, can cause problems for both cancer patients and diseased non-cancer patients. Thus, MDR can involve cancer cells, as well as damaged, non-cancerous cells (e.g., cells infected with pathogens including virus and bacteria). The emergence of the MDR phenotype is the major cause of failure in the treatment of infectious diseases (see Davies J., Science 264: 375-382, 1994; Poole, K., Cur. Opin. Microbiol. 4: 500-5008, 2001). Similarly, the development of multidrug resistant cancer cells is the principal reason for treatment failure in cancer patients (see Gottesman, M. M., Ann. Rev. Med. 53: 615-627, 2000).
Multidrug resistance is multifactorial. The classic MDR mechanism involves alterations in the gene (by gene amplification) for the highly evolutionarily conserved plasma membrane protein (P-glycoprotein or MDR 1) that actively transports (pumps) drugs out of the cell or microorganism (Volm M. et al., Cancer 71: 3981-3987, 1993); Bradley and Ling, Cancer Metastasis Rev. 13: 223-233, 1994). Both human cancer cells and infectious bacterial pathogens may develop classic MDR via mechanisms involving overexpression of P-glycoprotein (both messenger RNA and protein) due to amplification of the gene encoding P-glyocoprotein. The overexpression of P-glycoprotein mRNA or protein in MDR cancer cells or pathogen-infected cells is a biological marker for MDR. Diagnostic tests and therapeutic methods have been developed that make use of the overexpression of P-glycoprotein marker to diagnose and to treat MDR cancer and pathogen infections (Szakacs G. et al., Pathol. Oncol. Res. 4: 251-257, 1998). However, because various normal tissues express different amounts of P-glycoprotein, there are significant problems with side effects, as any therapy that targets P-glycoprotein on the cell surface of MDR cancer cells, would also affect those normal tissues that also have a relatively high level of P-glycoprotein expression, such as liver, kidney, stem cells, and blood-brain barrier epithelium.
“Atypical MDR” is a term used to describe MDR cancer cells or pathogens where the mechanism of multidrug resistance is unknown, novel, or different from the classic mechanism involving P-glycoprotein. For example, human lung tumors are multidrug resistant but do not have alterations in P-glycoprotein (see Cole S. P. et al., Science 258: 1650-1654, 1992). Rather, they express another drug transporter (the multidrug resistance protein or MRP1). A new mechanism of MDR was recently described that involves Lung Resistance Related Protein, which is a marker for this type of atypical MDR (Rome L. H. et al., PCT Publication No. WO9962547). Some other atypical markers for MDR include MRP5, which is a novel mammalian efflux pump for nucleoside analog drugs (see Fridland and Schuetz, PCT Publication No. WO0058471) and certain sphinogoglycolipids (see U.S. Pat. No. 6,090,565). Thus, there remains a need in both humans and animals for treating, detecting, preventing, and/or reversing the development of both classical and atypical MDR phenotypes in cancer cells and damaged non-cancerous cells, regardless of how the MDR arises (e.g., naturally occurring or drug-induced). In addition, the ability to identify and to make use of reagents that identify MDR has clinical potential for improvements in the treatment, monitoring, diagnosis, and medical imaging of multidrug resistant cancer and multidrug resistant damaged cells.